The present invention relates generally to the solar cell art and, more particularly, to a monolithic thin film solar cell in which a plurality of photovoltaic regions are connected in series through the film itself.
In the past, arrays of thin film solar cells have been fabricated by depositing each layer of the cells, including the photoactive layers, in preselected patterns. Alternatively, the layers have been patterned after deposition by removing portions of the layers between cells. The resulting cells are connected together externally to form solar arrays. Examples of arrays constructed in this manner are described in: Hanak "Monolithic Solar Cell Panel of Amorphous Silicon", Solar Energy 23: 145-147 (1979); Borden U.S. Pat. No. 4,278,473; and Hanak U.S. Pat. No. 4,292,092. Such arrays are generally rather expensive and difficult to manufacture, due largely to the steps required to pattern the photoactive layers into discrete devices. The patterning process also significantly reduces the active areas of the cells.
Another form of thin film photovoltaic device is described in Kuwano et al. U.S. Pat. No. 4,281,208, wherein one of the disclosed embodiments has an unpatterned active layer containing a number of photovoltaic regions. Electrical interconnection is made beyond the edge of the active layer. The structure is easier to manufacture than those described above, but is limited in size by the sheet resistance of its electrodes because current must be conducted to the ends of the cells where interconnection is made. The sheet resistance can severely attenuate any portion of the output signal generated at the interior of the panel, making the disclosed structure impractical for most uses. The Kuwano et al. patent also discloses another arrangement in which the active layer is patterned to permit connection at the interior of the panel.
Therefore, it is desirable in many applications to provide a thin film photovoltaic device wherein the active layer is continuous and unpatterned, yet the photovoltaic regions of the film can be easily connected in series.